How to turn On/Off a +5vcc power?

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I have a set of sensors and actuators all operating at +5v and draw 10mA to
680mA current.
My microcontroller will stwitch these units  ON or OFF in various
configuration. My microcontroller has enough output port to drive switching
circuits.

How can I switch these unit ON/OFF without using mechanical relay?
What is the electronic equivalent of relay ? (May be FET/MOSFET ? How to
drive them?)



Re: How to turn On/Off a +5vcc power?


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MOSFETs are good start. Try something like a MTP2955, IIRC it has quite a
low on resistance only about 0.2 ohms and a threshold voltage of about 3
volts. Its the cheapest MOSFET I can think of. This is device is a
PChannel device so let me see... tie the source to the 5V, the drain to the
Vcc of the things you want to drive and as for the gate, attaching it to the
output pin of you MC you give you what you want. Driving the line high should
turn it off and driving it low should turn the mosfet on. Depending on the
configuration of your MC, you may need pullup a pullup resistor at the
output pin of the MC.

I think my advice is correct, but don't take my word on it. Feel free to
get a second or third opinion.

--

Wing Wong.

Re: How to turn On/Off a +5vcc power?


There's nothing wrong with using discrete mosfets for this but if you
want some of the work done for you I have found BTS 612 N1 from Siemens
handy for similar applications. they need no extra components. A couple
of things to watch with this device: they shut down (brownout detection)
if the supply goes below 5V. Also if your processor is 3.3V that is
right on the edge of the turn on threshold, but I find they work with my
3.3V processors.



Johan Harold wrote:
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Re: How to turn On/Off a +5vcc power?


If you use a power MOSFET, put a 100R resistor in series with the gate.
This prevents ringing at switchon due to the high gatd capacitance of
power MOSFETs


Johan Harold wrote:
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Re: How to turn On/Off a +5vcc power?



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Check out Fairchild's FDG312P. Rds(on) = 0.18ohms @ Vgs = -4.5V, Vdss max =
-20V, Id = -1.2A
and it's in a SC70-6 package. Sneeze and its gone.. 8-)



Re: How to turn On/Off a +5vcc power?


On Monday, in article
     dmmilne_REMOVE_@ozemail.com.au "dmm" wrote:

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Or even Fairchild FDV range logic switching FETs in SOT-23 packages

                 Rds    Id      Id (pulsed)
        FDV304P  1.1R   460mA   1.5A         (4.5V Vds)
        FDV302P  10R    120mA   500mA        (4.5V Vds)
        FDV301N  4R     220mA   500mA        (4.5V Vds)
        FDV303N  0.45R  680mA   2A           (4.5V Vds)

Gate switching < 1.5V so ideal for low load switching in ONE device.
I tend to use FDV304P and FDV303N for lower Rds and higher Id

Available in small quantities Digikey, Farnell......

--
Paul Carpenter          | snipped-for-privacy@pcserviceselectronics.co.uk
<http://www.pcserviceselectronics.co.uk/ PC Services
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Re: How to turn On/Off a +5vcc power?


The others have responded regarding solid state switches (MOSFETs would
be my preference, too, though a ULN2003 array would take up less space
if you need more than one or two), but to add to the confusion: is there
a reason to shy away from relays? If only 680mA you could probably get
away with smaller reed relays. You can't hear them, they last for a lot
of switchings, and they don't need heat sinks. One thing, though, is
that you can't always drive a bunch of them at the same time from your
MCU ports. One at a time is usually okay, but of course, check the specs
to be sure.

-- Gordon


Johan Harold wrote:
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Re: How to turn On/Off a +5vcc power?


On Mon, 29 Aug 2005 19:27:37 +1000, the renowned "Johan Harold"

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Yes you can use a logic-level MOSFET (p-channel for switching +5V or
n-channel for switching the ground). There are some nice dual
low-Rds(on) ones in small 8-pin SMT packages.

Take care with bypass capacitors on the switched side. These parts are
so low resistance that if you switch them quickly the bypass caps on
the switched side can put a glitch on your unswitched power supply.  



Best regards,
Spehro Pefhany
--
"it's the network..."                          "The Journey is the reward"
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Re: How to turn On/Off a +5vcc power?



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What are the sensors and actuators? Can you get away with a cheap
trasistor?

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